I just wanted to drop a line about an upcoming change: We are working on the mechanic of the (Epic) Explosive Damage feats. It is planned to replace the current caster level based damage bonus with a percetage damage boost. The reason for this change is that the current mechanic leads to very varying effects on different spells. A single hit spell - like Orb of Cold for example - just gets the bonus once so the overall damage boost is pretty low. A multihit spell - like Scorching Ray - on the other hand gets the boost on each hit which leads to the strange situation that the bonus damage even exceeds the regular spells base damage. In some cases - like Flamearrow or IGMS - we adjusted the bonus damage within the spellcode to circumevent this problem. That is a very unsatisfying solution though because it requires adjustments within each multihit spell scripts. Another drawback of this solution is that you as a player can't really retrace what the Explosive Damage feats are doing acutally. That being said we believe that a percentage boost is the best and easiest solution.
We are aware of the fact that this change might lead to a reduction of the spelldamage in some cases and increase in other cases. After the rollout of the change we will evalute it's impact and make adjustments if necessary.